Heat treatment systems are used for heating semiconductor wafers to a desired processing temperature for oxidation, diffusion, chemical vapor deposition (“CVD”), atomic layer deposition (“ALD”) and/or other processes. During these processes, wafers are typically heated in a reaction furnace, either individually or in groups. To simultaneously heat multiple wafers, a batch of wafers is loaded into a wafer holder, such as a wafer boat, and the loaded wafer boat is inserted into the reaction furnace. The reaction furnace then heats the wafers and the wafer boat to the desired processing temperature. In addition to heating the wafers, certain heat treatment systems are also configured to process the wafers at a pressure below atmospheric pressure.
One challenge associated with heating the wafers in a heat treatment system is the amount of time required for the wafers to reach thermal equilibrium at the desired processing temperature. A conventional low temperature reaction furnace, for example, can take approximately one to two and a half hours to heat a typical batch of 300 mm wafers from room temperature (e.g., 25° C.) to a processing temperature of 75° C. A typical batch can include 150 wafers, and accordingly, one cause of the prolonged heating time is the substantial thermal mass of the batch of wafers combined with the wafer boat. One approach to expediting the heating time is to rapidly increase the heat transfer rate to the wafers. However, if the wafers are heated too quickly, the wafer temperature may overshoot the processing temperature, which extends the time required to stabilize the wafers at the processing temperature. In addition, overshooting the processing temperature can damage the wafer structure or materials as well as adversely affect the subsequent processing steps.
Another approach to addressing the foregoing challenge is to heat wafers individually. Heating wafers one at a time, however, will also not likely increase the speed of the overall process because loading, heating and removing individual wafers can take significantly more time than heating a batch of wafers. Accordingly, the amount of time required to heat a batch of wafers or a single wafer can significantly restrict the throughput of conventional heat treatment systems.